Recovery of tin from ores and the like



Patented Mar. 1 1932 iimmxtrvnvesmonn nni-indie: rrrzALIs KIRKPATRICK idem, on; 7'

" a I L N ,amtelv 'i-- g r a axoovrcaxon m ritonoREs nn THE. LIKE No Drawing, n piicatitn 'fiiaqune 4,1928, Serial No. 2821881, and. in Great Britain A ril 4, 1928;

This invention comprises improvements in the extraction of tin; from ores and the "like.-

- The term ;ores and thelike is intended. to include ores, concentrates, tailings andfby- 1 s'products which carry tin in commercially valuable quantity. I a F 1 According to the .inventiona process for the recovery of tin-'from' ores and the like is characterized by convertingthe tin therein *10 to the form of a sulphideof tinandsubmit ting the-tinsulphideto an-oxidizin'g-gas 'cur- I rent at a temperature sufficient to oxidize the I I t n sulphide, the oxidlzin'gga-scurrent-be ng;

0t sufiicient velocity" to carry the resulting Q tin oxideaway from't'he remaining-material of the ore or the likein'the form 'oii iiuine,

The fumeflmay be separatedjfrom the' gas current and collected by any suitable means, such as by'd'eposition', filtration-in baghouses,

and the like methods. I a I .j

The tin may beconverted to sulphide in several ways such as by the use of hydrogen :sulphideas a sulphidizing'r'eagent. In this case-the reagent I provides both thereducing and, the sulphidizin'g agents (asmay beindicated by-theequation 'Y l Sn0g+2HgSSnSfFQPLQ),j I A temperature-of dull redness issufficient to bring about the result. p e i 7 Alternatively, the tin may be vconverted to sulphide by treating it with: a sulphidizing reagent such as pyrites orssulphur vapour in the presenceof. a separate reducing agent,

In: one formv of a the process, the sulphidiza tion of the ore is eitected firstand. theel-imination of the tin asoxide in a separate subsulphidization step'is first app-lied to'a charge of saidore or. th'e like to iconvert the tin and arseniczto'sulphide at a suflicienttemperature touvolatilize and remove {the -arsenic, and, thereafter the tin. iseliminated as oxide fume by 1 applying. an oxidizing gas current to the hot'charge;

{operation ,7, l

-It is necessary thatithetin-bearing. ma- 1 fterial and the other components of the charge shall be in a state of suflicientlyfine division.

for example carbon or carbonaceous matter, 7 v

Incertain.cases,howev er,. foiiexamplewhen zation under such conditions, are present in 'negligible quantity,i the sulphidizing and oxidizing oper'ations may. be combined; In

the-presence of a'sufiiciency of sulphur-yieldingmaterial andcarbon the sulphidizing'of the tin here appears to precede its re-oxidation into tin oxide fume, r t A-furtherfeatureof the invention,.therefore," comprises a processas above described 130 whereinthereducing agent is solid. carbonaceous matter mixed with the ore, the sulphidiz- 7 :ing reagentiis a solid body, for example iron 'pyrites mixed with the ore, and the'oxidizing j gas current is applied to this mixture which f f is maintained at the necessaryv temperature,

so that theisulphidizing and oxidizing; reacy tions proceedin such manneras effectively-to eliminate the tin as'oxide' fume in one We have obtained good results from Cornish ores [and concentrates which havebeen .75 I

ground to pass through a 100 mesh;(I..M,M.)

' screen, although a somewhat coarser powder give "g'ood'results' according to the character ofthe' materialunder treatment. a v V If the tin be present'ascassiterite and carbon be the reducingv agent employedfihetype of the reactiomin its simplest form, be indicated by the equationi r s loss2+2o=snamoos The tin oxide,ior' cassiterite, is converted to sulphide with commercial completeness; at atemperature of about 750800- (1., careirbe- J ing taken that: the temperature during the sulphidizing stage does not reach: that at vwhich sulphide of tin is sensibly volatile.

If other substances-be present inthe oremaf terial which arezcapable of absorbing o'r-com;

bining with sulphur under like conditions, i

a" further sufliciency ofthe sulphur yielding material. must be added, .to ensure that allthefitin shall .be converted to sulphide- If arsenic be present in; the ore it will 'beielim- .inatedduring thissulphidizing step in the" form of: yellow; or. orange sulphide of'arsenic which may be readily condensed and recovered in a suitable condensing item attached to the sulphidizing retort, furnace, chamber or vessel. If the sulphidized product is not to be submitted immediately to the oxidation blowing step it should preferably be cooled out of contact with air. I

The physical condition of the sulphided product isof importance in the operation of our process since the tin sulphide produced as above subsequently requires to be brought into ready and efiective contact with the oxidizing current at a temperature which permits-of its combustion. The texture of the sulphided product must therefore be kept s'ufiiciently open and porous in order to permit the tin sulphide to burn readily to oxide, and to allow free egress to the-resulting tin oxide fume. Tin oxide is non-volatile at the temperatures we employand although by burning the sulphide, as described, the oxide forms a cloud of highly divided particles,

' i. e. a fume an articles of the oxide arrested b the mass of the char e ma tend y e y toremaintherein and to some extent, therefore, to become lrrecoveraole by further blow-' ACCOIdlD to a further feature of the m-' vention, therefore, the ore before the oxidizing step may belinely divided and made into anopen porous charge by incorporation with a material such as will impart an open and porous structure to the resultant charge. For example, the carbonaceous materialpemployed in the sulphidizing step may be cok- -ing coal which intumesces and gives a porous character to the charge before it is submitted tothe oxidizing step. Several other substances are known for such purposes, such as mixtures of refractory clays with sawdust, orthehke. c, I We may use bituminous coal, and a sultable binder such as tar or pitch, for agglomerating the charge and then'submit the product to the coking (and sulphidizing) operation. The proportion of coal used or other suitable carbonaceous material, will vary with the. nature of the ore, its tin contents, etc. We have obtained good results by using from 40% to 80% of crushed bituminous coal and a tar binder to themixture of the tin-bearing material with the sulphur yielding substance; we do not how-ever confine ourselve-sto these proportions, as in every case experlence wlll determine the best and most economical quantity of coal or carbonaceous substance necessary to afiord the required porosity to the charge to be blown.

The coking and 'sulphiding operations thus take place in the same retort, orapparatus. The main carbonization of the coal and binder takes place at a lower range of temperature, say about 400-500" C.,=the ar-r senicpresent is next eliminated as sulphide, and the sulphidizing of the tll'l is completed at a temperature range between about 700- 800 O.

In the equation above given the tin sulphide produced is shown as stannic sulphide, S113 but stannous sesqui-sulphide, Sn S or stannous sulphide, SnS, may also be produced by the reaction and either orfall of these are suitable for the purpose of our invention.

In agglomerating the charge of ore or the like with the sulphur-yielding reagent by means of carbonaceous matter and a binder,

and coking in order to obtain the necessary porosity, briquetting may be employed. The coked and sulphidized briquette product is thereafter blown as before described in a suitable furnace at the temperature required to burn the tin sulphide to oxide fume.

. The size of the briquette must be chosen so that its tin content may be eliminated with commercial completeness. The size may therefore vary with the nature and tin content of the ore, the proportion of the carbonaceous matter employed, the open-mass of texture or porosity, and so on.

If found desirable the coked and sulphided briquettes,after cooling in a neutral atmosphere, may be brokenor roughly granulated to a size which permits the readiestelimination ofthe tin. These factors (as also the depth of the charge .uponthe blowing grate or series of grates) will best be determined in each caseby experiment, the criterion being the avoidanceof recondensation or arrest of more thanv av commercial minimum of Sn0 fume in the charge itself. V

' The carbon in the coked and agglomerated 'mass plays no chemical partin the oxidation .reaction beyond consuming its equivalent of the oxygensupplied by the oxidizing current, but it plays an important partiinc providing a matrix or skeleton to hold back inert finelydivided material, such as gangue, oxide of iron, ash etc. from removal by the gas current and thus to minimize the contamination of V on a grate through which an oxidizing current or blast of suitable velocity may beinduced'by suction, bymeans'of asuitable fan or the'like, which may also be used to force the fume and gas passing through it into the filtration or baghouseapparatus, which, when employed, is the last item in the circuit from theblowing-grate or. furnace and may be 6O from the Greevor mine, Cornwall, carrying constructed similarlyto the apparatus commonly used inthe production of zinc oxide from the blowing of zinc ores.

' be conditioned by the depth and op'en-ness of the-charge on the grate usually a negative pressure of one or twoinches of-water in the V induced current will be suflicient but the required pressure may easily be modified or regulated by the operator ii -charge of the grates. I A combustion chamber may be .added immediately beyond-the grate exit which-may ply. It may if desired be independently heated, but if properly proportioned it will reach a sufficient temperature by virtue of the function without further fuelexpenditure.

Its object is to complete the oxidation of any carbonaceous matters or traces of tar which may be liberated from the charge on the grate.

25 i flThe depth of the charge on the grate is.

residues fall, or are stirred by the operator,

through the grate; a fresh charge is introduced from time to time as necessary through a charging door above the grate. f 1 Additional fuel may be added if required or if desiredalternate layers of fuel and charge may be added. In any event the blowing operation is first started by provid-' ing a glowing bed of fuel upon the hearth to receive the first charge.

In place of a stationary grate or series of grates, a mechanically-operated hearth of chain, or other type, or pallets, may be used to ignite and blow the tin from the charge. It will be understood that in certain cases, i. e. where the constituents of the charge con tain no metals other than tin capable of elimination in the form of fume,it may be found unnecessary to carry out the coking and sulphidizing operation as a separate step. In.

such cases the briquetted charge admixture may be fed direct to the blowing hearth under conditions suitably regulated by the operator in charge, provision being made to. ensure the completeoxidation of the volatile hydrocarbons. v The following is anexample-of oneoperation in accordance with the process s I Example I A sample of finely ground tin concentrate 31.4% of tin" as cassiterite, was mixed with 80% of its weight of pyrites ground to pass a screen having 80 meshes (I. M. M.) per lineal inch-and the mixture'was then briquetted with be furnished with an extra regulated airsupheat developed in the blowing grates, and

j in the usualmanner." s

until nearly all the volatile hydrocarbons were eliminated; the heat was 'theniraisedto' -about 750?. Q..O C]. during. which period the arsenic present in the concentrates (about 2.5%)" was volatilized as an orange yellow sulphide; and readily condensed-and collected in a condenser tube. 1 I G l A layer of carbon (coke) was placedupon a suitable enclosed furnace grate and'ignited. The sulphidized briquettes (in this case cooledout of contact with air) were roughly broken and then charged on to the glowing1 coke through which a sufficient currentof low-pressure air was induced by a fan to ignite and blow the charge. V

The tin was rapidly'eliminated as. tin oxide fume which was collectedin a flue andbag-c8 house system and: condensed as a white con- 'centrate of ne arly pure stannic oxide.

After blowing, theresidue left, on the grate assayed and-i showed 98.2 %,of the tinlin thciorigina-lv concentrateto jllave been slim- 59 inated.

An alternative procedure for eliminating the-tin, inthe form oftin oxide/fume, from thesulphidized product consists reducing thelatter to a fine powder] and feeding ,it22 into the flame of a strongly oxidized blast,

suchas may be furnished by the combustion of powderedlfuel, or of gas, or other combustible. vapours ;-or.again the finely-.pow-

dereid sulphidizedp'roduct may be. injectedFi1: with air into achamberheatedto a suflicient V 7 temperature to causethe tinFsulphide to :be converted into tin oxide fume."

I It is obvious that several methods may be adopted for eliminating tin as oxide fumefil .withoutdeparting from the nature of our invention.

One advantage of our process is that a large proportion of the tin oxide fume is recovered in a form which. may be used for 21 enamelling or for such other purposes as require an opaque white oxide of: tin. Any small'proportion of impurity such as ash from the gratewhich maybe mechanically carried over with the oxide,"m'ay be sepa- 1 rated therefrom by. bolting, ,levigation; or

other known means; or alternatively the oxide of tin may be smelted to metallic'tin 1 Weclaim ze 1. A processfor theextraction of'tin from.

ores and the like comprising the steps of convertingthe tin-to sulphide by'treating it with a sulphidiz'ing' reagent in the presence x of a separate reducingagentand submitting the :tinsulphide to an'air current at a temperature suflicient t-ooxidize' the tin sulphide but insufficient to cause'fusionof the charge,

the air current jbeingl of sufficient velocityto carry such manner as effectively to liberate the tin as oxide fume in one operation.

3. A process for the extraction of t1n from V ores and the like as claimed in claim 1 comprising the steps of admixing the ore first with coal and briquetting and coking the mixture before sulphidizing.

i. A process for the recovery of tin from ores and the like comprising the steps of admixing a charge of the material to be treated with carbonaceous material and a solid sulphidizing reagent,heating the mixture in an open porous condition, and passing air therethrough in suchquantity that oxidizing con ditions are maintained throughout the charge and tin as oxide fume is liberated and carried away in the air current.

5. A process for the recovery of tin from ores and the like comprising the steps of admixing a charge of the material tobe treated with carbonaceous material and a proportion of pyrites, heating the mixture in an open porous condition, and passing air therethrough in such quantity that oxidizing conditions are maintained throughout the charge andtin as oxide fume is liberated and carried away in the air current.

6. A process for the recovery of tin from ores and the like comprising the steps of admixing a charge of the materialto be treated with carbonaceous material and a solid sulphidizing reagent, heating the mixture in an open porous condition to a temperature of at least red heat but not sufiicient to produce molten slag from the charge, and passing air therethrough in such quantity that oxidizing conditions are maintained throughout the charge and tin as oxide fume is liberated and carried away in the, air current.

7 A process for the recovery of tin from ores and the like comprising the steps of admixing a charge ofthematerial, to be treated with carbonaceous material and asolid sulphidizing reagent, heating the mixture in an open porous condition to a temperature of approximately 7 50850 (l, and-passing air therethrough in such quantity that oxidizing conditions are maintained throughout the charge and tin as oxide fume is liberated and carried away in the air current.

V 8. A process forthe extraction of tin from oresv and the like, comprising the steps of admixing the ore, containing tin in the form of mixture upon a grate in a stream of air such as to maintain oxidizing conditions throughout the charge and to carry away tin as oxide fume from the charge.

9. A process forthe extraction of tin from ores and the'like, comprising the steps of admixing the ore, containing tin in the form of cassiterite, with carbonaceous material and pyritic material, and burningthe mixture upon a'gratev in a stream of air such as to maintain oxidizing conditions throughout the charge and to'carry away tin as oxide fume from the charge.

In testimony whereof we have signed our names to this specification.

HENRY LIVINGSTONE SULMAN.

HUGH FITZALIS KIRKPATRICK PICARD.

cassiterite, withcarbonaceous material and a solid sulphidizing reagent and burning the 

